The invention is based on the kinematics of a machine drive for the tool and work gear axes of rotation, the principle of which can be carried out on a machine which is discussed in U.S. Pat. No. 5,443,338 to Huber et al.
Practice has shown that when dressing the internally toothed tool with a dressing wheel coated with a hard material, which dressing wheel has a smaller contact zone than the width of the tool, problems arise when bringing about a desired change of the tool pitch angle with this contact zone during a freely running engagement. A change of the pitch angle in dependency of the dressing state and of the therewith changing profile shift between tool and work gear or dressing wheel is desirous, as it is described in U.S. Pat. No. 5,377,457 to Loos et al, in order to maintain the contact force balance during the freely running engagement.
When the contact zone between the dressing wheel and tool is shifted in the tooth flank width direction, then additional rotations occur. This means that the path of the contact zone differs from the path predetermined by the existing tool pitch angle. The dressing wheel is furthermore desirous of following the existing tool pitch angle during the freely running engagement. Thus, a calculated change of the existing tool pitch angle is not possible.
On the other hand, a freely running engagement between the work gear and the internally toothed tool has often advantages, since only as much material is to be removed from the work gear flanks as it is needed for a satisfactory operation of the work gear. Shorter machining times and longer tool lives result.